Reduction of Nitrogen Oxide by Zero-Valent Iron Fluidized Bed

• Main Authors: Chih-Yu Cheng, 鄭自祐
• Other Authors: S.S. Chen
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/9z44bw

碩士 === 國立臺北科技大學 === 環境規劃與管理研究所 === 93 === A novel research was conducted for the chemical reaction between nitric oxide and zero valent iron (ZVI). Because of the ZVI strong reducing abilities, we designed the Zero Valent Iron Fluidized Bed Reactor (ZVIFBR) to execute this study. Three different parameters: temperatures (673K, 723K, 773K), influent concentrations (700, 850, 1000 ppm), and ZVI dosages (0.75g, 1.00g, 1.25g) were tested in the ZVIFBR. According to the experiment results, we found that effluent concentration curves were related to operating times, and obviously could be divided into two sections. In the first section, the concentration curves are smoothly, but in the second section, the curves are steeper than those in first section. In the first section, at the same reaction temperature (773K), the influent concentrations by 700 came to 1000 ppm, the reaction rate increases about 43%, and at same influent concentration (700 ppm), the temperature by 673 came to 773K, the reaction rate increases about 15%. The relationship between pseudo rate constant kobs (s-1) and the reaction temperature are matched Arrhenius Equation. When ZVI weight by 0.75g came to 1.25g, the rate constant k (mole-0.4s-1) increases about 22%. The influences of reaction rate parameters are influent concentrations > reaction temperatures > ZVI weights. In the second section, the efficiency lowered down slowly with the operating time, this is because the ferric oxides gradually covered the surfaces of iron powders. In same influent concentration (700 ppm) and ZVI weight (0.75 g), the temperature through 673 to 773K, the break through time by 2491 sec increased to 3391 sec. The reaction rate equation includes two constants: k’ (rate constant, mole-1s-1) and kd (iron oxide constant,s-1 ), the two constants were related to reaction temperature, but not matched Arrhenius Equation at all, . XRD (X-Ray Diffraction) and ESCA were conducted to analyze the crystal structure and oxidation state of the reacted powders, several species were determined from the spectrum: Fe0 (ZVI), Fe2O3 and Fe3O4. Apparently, the chemical mechanisms of ZVI and nitric oxide are: (Equation 1) The utilization of ZVI also related to reaction temperatures, higher temperature more utilization, the reaction temperature from 673K to 773K, the utilization from 3.1% increased to 7.8%. The Capacity of De-NO per ZVI (mg-NO/g-Fe) is related to reaction temperatures too, the reaction temperature from 673K to 773K, the Capacity of De-NO per ZVI from 5.56 mg-NO/g-Fe increased to 62.37mgNO/gFe.